I've been playing with some of the small and quiet compressors lately, and this project has been about that kind of mid size unit that's for a daily use system. Cold, sure, but the emphasis is on both quiet operation, and a relatively low power draw.

Bigger compressors can get expwnsive to run and the small compressors can be very efficient in that way, so it's a good test of how small you can get away with, and still get cold enough to overclock really well.

Finally got the last of the compressors I needed. Ended up doing a quick test on a whole lot of them before I found an assortment that fit the bill. Had to be small enough to fit the compact design, large enough displacement for the job, and most important, quiet.
All different ones though. Wanted to see which would stay quiet under load, and if the slight difference in brand and CC's would make much of a difference, considering they're all around the same BTU rating, other than the larger displacement CPU compressor.
Specs so far
GPU compressors
Tecumseh 2.4cc low temp
Danfoss 2.6cc low temp
Huayi 2.9cc low temp
CPU compressor
Samsung 1/5hp low temp
Common condensor 12000btu/4
10 passes per gpu
12 passes for cpu
14" x 13" x 2.5"
Works out to the equiv. of 6x8" gpu and 8x8" cpu condensors
Custom case
12" x 15" x 20"
Central outlet for flex lines, will be designed for a PC case to go on top with room to go beside the lines with the PC side panel removed, or cut the PC case and have the lines inside.
I fabricated the case with metal I had here. Bit of a variety of pieces but it's all welded so nice and strong and ready for panels. Haven't decided completely yet, but I'm tempted to go with Perspex and have it a smokey or black finish.
Won't see the insides when it's done, but I painted the chassis for now. Nicer that way. It's all galvanised metal so it was awful to weld. Came out ok, and the ugly bits aren't visible anyway.
The case and compressors are a perfect fit. That is, all the room is taken up so no room for error. I'll have plenty for wiring but as far as temperature displays go I'm going to have to go flush mount. Only ones I can find are the awful PC case things :p but they're ok to -50 and they'll do for reference anyways. A real 4 temp display would be better but I can't find one that really suits.
The evaps are going to be a Chilly1 head for the CPU and a pair of @itor GPU evaps along with the modified Kayl GPU evap I made for that other test unit.
The ideal thing about this is that it's getting away from the multihead unit where you need to deal with balance and have a huge noisy compressor to go with it. A waterchiller was a thought, sure, but direct die is more ideal I think. Smaller compressors in multiples can do the same job while being quieter are more efficient.
I'm shooting for 200w per head on all 3 gpu, with the CPU evap tuned for 260 watts.
The temps I'm expecting on the GPU heads under load at 260w are similar to the test unit I built, around the -5c mark, but I think that with the temps you'll see on the GPU it will only OC to a level that would pull 200w.
I may just tune them a bit heavier, or right up to the 260w levelon the GPU's.
The CPU I want full coverage, and I'm hoping to see -20 or so at 260 to 300w. Haven't used a Samsung compressor before, but it's bone silent :D If it gives a decent level of cooling, and can remain silent at the higher load/backpressure, I'm a happy guy.
The condensor will be running either 9x120mm fans or 4x140mm fans. I haven't decided yet. Better condensor coverage with the 120's, and can run them slower for noise levels. 140's are naturally quieter but the sizing is wrong, and I have no room for shrouding so I need a full cover of fans for sure. We'll see how it works out. I still need to buy them, but will stick a barrel fan on for testing if I don't have them yet.
So far the CPU phase unit is together with the Chilly1 head. The 1/5hp compressor is set at 1-3psi unloaded, and with a quick Ďflame testí pushes the low pressure up to around 18psi. Frosting just at the compressor inlet with no floodback. Iím pretty sure that it has the capacity for 260w with that kind of pressure response but with a smaller compressor Icanít be sure until itís on the tester, possibly later tonight, possibly tomorrow.
I have the GPU lines left to assemble but the short flexís are done, just need the larger flex line installed.
the plan is to have the more flexible and smaller flex to the gpu's, with the heavier flex directly attached that can be shaped to the exact fit. Should be a good combination of flexiblity, size and vibration dampening.
That's as far as I've gotten. I'll update when I get more done, but it's pretty close and once the other lines are brazed I can finish up the insulation and get to load testing.
I did add one accumulator per GPU due to the smaller pipe size and short suction lines. I didn't add one to the CPU line due to size limits, but it's got 3/8 pipe along with a long 5/8" flex, so volume isn't the issue like on the GPU lines.
So here is the current setup. The two-part flex lines worked very well, but in future i think it would be much easier to just use a smaller flex on the GPU's in one piece. This setup is really cool though, allows for a more solid run to the card, then a really flexy line for the finer adjustments for install.
I added a basic barrel/cube fan for testing until I've got the flat axial fans here. Runs quiet enough though not what I want, around 200cfm at low speed.
They're all maxed out for load now, ready for load testing.
It's funny that the Tecumseh is the smallest of the compressors but really the noisiest of all 3 gpu compressors. Figures though, Tecumseh always seems to be the loudest of compressors in any size and capacity range.
The Danfoss is the quietest of course :D but the Huayi isn't that far behind, and it's good to see since in actual production it could be a very inexpensive alternative. Knowing it's also capable at higher loads, I think it's a winner all around.
The Samsung isn't bad for noise either considering it's higher capacity. Under load is where it's most meaningful. Looking forward to finding out how much the noise increases with load.
So just one initial load test done, and it's about what I expected.
Idle/unloaded, around -30c with 8psi low.
260w worked :) and sat around 40psi low.
The front temp is the evap itself, and the back one is the actual plate temperature of the load tester. About a 20-25 degree difference across the thermal paste, so heat transfer isn't too bad. At that heatload I expected something in that region.
That was on the larger of the GPU compressors, the Huayi.
Results on the CPU unit...
So -19 at 300w now that I have the tester to set it up :)
Should be fine for Quad core now, and the -20 range is great :D
Really quiet even with load on it, still under 20db.
Running about 18psi low at full load
I don't have any real information on how high GPU heatload will go, and I haven't seen much of anyone showing GPU temps vs evap temps on a single stage cooler. Would be great to compare this info with actual installs.
Comparing results against water, assuming the full 260w, means a minimum of 20 to 25 degrees colder gpu temps :) which I think would translate into much better OC results. I think the difference would be much higher but if you have a high end water setup, able to maintain a 25c block temperature even under full load, how much higher would the gpu temp be? 20c? 25c? If so, and the gpu temp would average more like 50c at best under load with a high OC and high Vcore. A quick look at someone's 'roundup' of blocks seems to indicate 50c gpu temp at best with an overclock on 480gtx but no indication if that's under load.
Would like to see how it compares that way to water, get an idea of how beneficial this kind of small yet high capacity setup would be.

As far as power consumption goes, I plugged this thing into the power meter and recorded the draw.

700w startup, which dropped to about 550w right away when cooling down, settling to around 480w running all four systems. I estimate that with the thing cooling full load PC stuff, about 600w max.

not bad though. 600w of power, to cool close to 1000w of heat :) Refrigeration stuff in the small sizing is really efficient. Close to 200% efficiency with these small compressors.

It's actually really easy if you can get a portable AC unit. Especially the square looking Danby ones, they build them so it's really easy to take apart without taking out the gas and if you're really careful, you can bend the tubing to get the evaporator (it's up top) to bend flat and fit in a plastic tub :D I made a little guide once, will have to post that too :)

OK, some results from the GPU heads, with some tuning updates.

I ended up going with 300w on the CPU head, for quad core tuning.

275w is about what I've seen as a max for this type of cooler, but 300w means there's room for error, and if you have a 'bad' chip that pulls more heat, you're covered.

The GPU's are at 225w. Some of the new stuff, like 480's (gtx) are something like 100w stock load, but will double that if you overclock and give a bit of a boost to the core volts.

So 225 should give a bit of room to overclock to about the max you'll get with the mildly subzero temps.

CPU...

Samsung 1/5hp around 5cc (no spec found) runs around 10-15db unloaded, and 15-20db load, or about the same as a quiet 120mm fan :)

300w -19c and -38 0w

GPU's tested to 225w

First is the best :D Danfoss 2.4cc 1/10 to 1/8hp runs 10-15db idle and load.

So around -18 idle and -10 load. Ideal for GPU, since it's less likely to freeze up when the GPU isn't being stressed.

Next, the Huayi 2.9cc 1/8hp running 20ish db idle/load

-9 and -22c so still pretty good :)

Last and worst, Tecumseh 2.3cc 1/12 to 1/10hp 15-20db idle, 20-25bd load :p
-7 load and it was hard to tune for 225w. Just didn't like it there. Bit small? Maybe just too far out of spec.
Was around -30 idle as well, didn't bother with a pic, it's getting changed out.

So that's a basic idea of what the smallest of compressors that you can get away with will get you for temps, and it's not bad at all. For a CPU compressor the 1/6 to 1/5hp range is about -38/-10 idle to full load. Pretty good for a near silent phase cooler.

The Danfoss series IS the best for noise overall, and the 1/4 to 1/3hp compressors aren't much louder than the ones here, but they're harder to get for a reasonable price so they come when they do.

That 2.4cc Danfoss in the GPU loop was the best of all for real world. Colder under load but warmer with no load is perfect, making for far less need for serious insulation. Still needs the basics but when you're under -35c you need to really pile it up. This makes it much easier.

GPU is the worst since the idle of a GPU is so small compared to a cpu, so I like the result there.

The Tecumseh was a pain, it's just too small for really nice tuning. Louder than the rest too. Never liked them for that.

The cheapo chinese compressor surprised me, it's not bad for a 'no name' generic thing, and a good alternative to the better ones. Worked pretty good, and wasn't too loud.

For those looking at getting into building a cooler themself, these small compressors are available in water coolers in various sizes, though usually the 2.3 to 4cc max. Still very useful for dual core and some for quads.

I'm going to swap out the Tecumseh for another compressor I have here that's a 2.6cc. I'll test and post that, but it should be close to the Huayi compressor.

When that's done it's just panels and some temp displays and it's ready to go :)

Honestly it's way harder to make a quiet cooler work well than to just jam a huge Rotary compressor into it. So many little details and some more involved tuning to get it right.

Seeing -10 or so under load with them is awesome though :) I was thinking -5 at best. They're running more in spec now though, like what they were designed for, so it's probably why they're working so well. 260w was a real struggle for them and the temps kind of showed it.

I'll see if I can get the other compressor in there to replace the Tecumseh tonight but with Xmas here, and being so tired (shopping tires me out :p ) I don't know.